Acrylic syrups have transparency, and cured products obtained by curing the acrylic syrups easily adjust adhesive strength for various base materials and have been used for various uses such as an adhesive sheet, an adhesive film, a protective coating, a foam, and an adhesive.
Examples of a polymerization method for preparing the acrylic syrup include a solution polymerization, an emulsion polymerization, and the like, and the solution polymerization has a problem in that an organic solvent remains in the acrylic syrup, which may generate odor, fire, explosion, and the like, and the case of removing the solvent by evaporating the solvent into the atmosphere causes atmospheric contamination, which is hazardous to the environment. Further, in the case of the emulsion polymerization, an organic solvent is not used, but after a polymer is synthesized, the polymer may not be used as it is, and an additive such as a neutralizer, a wetting agent, a thickener, and a disinfectant needs to be added in a large amount, and the addition process is also complicated, and a large amount of waste water is generated because a large amount of water is used in the process of washing a reactor after the synthesis is completed.
For this reason, eco-friendliness, high yield, and economic efficiency may be achieved by using bulk polymerization, and examples of the bulk polymerization include bulk thermal polymerization which is initiated by heat or bulk photopolymerization which is initiated by light.
In the case of the bulk thermal polymerization, the productivity is low due to the relatively slow reaction rate, and the polymerization is continuously performed to some degree at normal temperature even after the temperature is lowered, and as a result, physical properties may vary.
Meanwhile, in the case of the bulk photopolymerization, the productivity is high due to the fast reaction rate, but since the reaction may explosively occur and it is difficult to uniformly prepare an acrylic syrup having a desired level of conversion rate, a molecular weight adjusting agent and the like have been essentially used in order to solve the problems. However, since the above-described molecular weight adjusting agent and the like remain in the prepared acrylic syrup, and still remain even after the acrylic syrup as an adhesive film, a protective coating, and a foam is applied to a product, there occurs a migration phenomenon in which a molecular weight adjusting agent having fluidity, and the like migrate to a surface of the product, and since residue of an adhesive, dirt, and the like may be generated, there is a problem in that the surface appearance and the performance of the product may deteriorate.